Uniform energy supply



g- 27, 1946- H. A.- STRICKLAND, JR 2,

UNIFORM ENERGY SUPPLY Filed June 28. 1944 I: INVENTOR HAROLD A.STR1CKLANDJR azz. fi fw ATTORNEY Patented Aug. 27, 1946 2,406,715 UNIFORMENERGY SUPPLY Harold A. Strickland, Jr., Detroit, Mich., assignor, by mesne assignments, to The Budd Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 28, 1944, Serial No. 542,568

9 Claims.

This invention relates to a circuit and associated apparatus for maintaining uniform the energy input of a power consuming device, such as a furnace.

In various types of equipment, particularly induction furnaces, it is important from th viewpoint of constant temperature requirements of many types of workpieces as well as .efiiciency and costs that the input of energy into the furnace be substantially uniform irrespective of source voltage variation, this being of considerabl importance when a series of similar unit loads are being successively treated by the furnacex In-accordance with the present method I utilize voltage of the source current to determine the amount of energy transferred to the load.

In accordance with the statement as hereinabove made, an important object of the invention is to provide means which are effective to control the amount of energy received by the load so that the energy input is substantially uniform for successive loads. Anot er object of the invention is to provide control means for obtaining uniform load heating which is dependent upon the voltage of the heating current. Still another object of the invention is to provide means for uniform load heating which is independent of rotating or movable mechanical parts. An object also is to provide control means that functions through a limited number of electronic devices. An additional object is to provid apparatus for uniform load heating which may readily be adapted to usual standard commercial heating equipment. Other objects of the invention will appear on consideration of th invention as hereinafter described and as shown in the accompanying figure.

Referring to the figure, there is indicated diagrammatically a circuit applicable to a timer of an induction heating unit although the invention is not limited to this particular use. The circuit may be roughly divided into five sections indicated by the capital letters A, B, 0, Band E, the letter A referring to the rectifier section, the letter B to the voltage control section, the letter C to the oscillator section, the letter D to the constant potential section, and the letter E to the amplifying section. Connection to the commercial power source is made at it, current being conducted through the transformer II to the bridge rectifier l2. The rectified current is led through conductor l3, variable linear resistor l4 and non-linear resistor I! to conductor l6. As is known in this art, thecurrent in a non-linear resistor such as Amperite which is iron in a rapid heat conducting atmosphere such as helium, varies as a power of the voltage. This power may be controlled to some extent, units being made having a power which may vary from one to five according to the formula EoaEa +K where E0 is voltage across the Amperite, Ea voltage across the inlet mains, and K a constant.' For the purpose of this invention it is assumed that th resistor has a variation of current in accordance with a value of n between 1.5 and 2.6. Voltage drop through the resistor l4 accordingly will vary in accordanc with the voltag impressed on the non-linear element l5 and utilization is made of this non-linear variation in voltage across the resistor l5 to cause a variation in frequency of the oscillator circuit C which will now be described.

The oscillator circuit section C is centered in the otcillator tube 20 which is of the complex type having anodes 2| and 22, control grids 23 and 24 and a single cathode 2'5 heated by a separate heater coil 26. As shown the control grids are connected to the point 21 intermediate the resistors l4 and [5 through resistors 28 and 29. The cathod of the tube is grounded and also connected to the point 3| on the side of the resistor l5 opposite from the point 21, or to the negative side of the circuit plate voltages for the units 2| and 22; and current for the resistor heating filament 26 is supplied from the power unit D. Use is made of resistors 32 and 33 to limit the power supply to the anodes. Also a capacitor 34 is placed between the grid 24 and the anode 2| and a capacitor 35-between the grid 25 and the anode 22. Anodes 2| and 22 are also connected by circuit conductors 36 and 31 to the amplifying branch circuit E.

The circuit D is more or less conventional in form utilizing a transformer 40 having primary coils 41 and 42, secondary coils 43 and 44 and 45. the anodes of a dual rectifier tube 46, the oathode 41 of which has its ends connected to the terminals of the secondary 44. The mid-point of the transformer secondary 43 and the cathode the resistor 52, resistor being in series with the glow tubes to secure the desired voltage point at the glow tube terminals. The one side of the rectified constant potential circuit is connected to the grounded side 0! the 0 section as at point Secondary 43 at its terminals connects to ll while the other side of the D circuit is connected from point I! to the conductor Joining the resistors 32 and 31 in the plate circuit of the section. There is thus provided a constant potential from the D load supply to the anodes of the oscillator tube. The secondary ll of the transformer 40 supplies current to the filament 2! of the oscillator tube.

A push-pull amplifier is utilized in connection with the oscillator and comprises two amplifying tubes 00 and 81, each of these tubes being provided with control grids B2 and SI and double shield grids 84 and GI as well as cathodes I! and 01 to independent heaters 88 and N. The heaters each are connected to the secondary ll of transformer 40 in the power supply circuit D. The control grids 82 and 83 are connected through capacitors Ill and II and resistors 12 and II to anode conductors 38 and ll of the oscillator circuit C. The cathode is connected through resistor H to the cathode 25 of the oscillator. Between capacitors HI and resistor 12 and capacitors II and resistor II the conductor leads to the cathode circuit through capacitors II and 18 respectively, Also between capacitors l0 and the control grid 82, the capacitor H and control grid 63, conductors, including resistors 11 and II respectively, lead to the cathode 25.

The anodes of the amplifying tubes are connected through the primary 80 of the amplifying transformer H, the mid-point of the primary having connection to conductor I2 Joining the shield grids of the amplifying tubes; The secondary ll of the amplifying "transformer 8| is directly connected to a synchronous motor II which in turn is operatively connected to the timer mechanism It controlling th switching contacts of the heating unit It.

The operation of the circuit may now be described. It may be assumed that power is being supplied the sub-circuits A and D from the line and consequently the oscillator tube 20 is transferring oscillations of a definite frequency depending upon the voltage across the resistor ii. The oscillations of the oscillator are moreover amplified and transferred to the synchronous motor which rotates at a speed corresponding to the frequency of oscillation. If a heating operation is in effect and the voltage is maintained constant through the heating operation, the synchronous motor will function-at a constant speed and thus heating input into the load will be at a constant rate. Further, should a series of workpieces be subsequently inserted in the furnace and the voltage remain substantially constant, the time period and the amount of heat transmitted to the successive workpieces would be uniform. However, if for any reason the voltage across the resistor [5 should change, the current passing therethrough will vary non-lin early, due to the fact that the resistance of Amperite varies non-linearly, producing a change in the voltage across the oscillator tube. A characteristic of the oscillator described is that the frequency of oscillation is dependent upon the voltage impressed through the circuit; consequently the frequency varies as the power of the voltage in the source circuit. Since the source circuit is applicable to the heating coil of the furnace it is apparent that the synchronous motor will rotate more slowly if the voltage is low and increase its rapidity of rotation as the voltage increases. This functioning of the synchronous motor consequently increases the time interval of heating for lower voltages and de- 4 creases the time with the power of the voltage for higher values. Thus the energy for a given heating interval will be approximately uniform irrespective of the voltage impressed upon the heating coil.

It is apparent that utilization is made in this circuit of devices and apparatus which are more or less conventional in nature such as the oscillator circuit, the power supply circuit, and the amplifying circuit, and hence modifications of these elements may be made without modifying or detracting from thewssential novelty of the invention which centers about the utilization of non-linear resistors for securing a uniform energy input in a serie of workpieces, independent of variation of voltage. Other modifications may be made, the limits of the invention being defined by the claims as hereto appended.

What is claimed is:

1. In energy supply means, a heating unit, a' source of power for said unit, a timerfor setting the time period of application of power to said heating unit, and means connected to said timer for modifying the timer period to compensate for changes in power source voltage, said means comprising a non-linear resistor connected to the power source, means for establishing a direct cur" rent voltage across said resistor, an oscillator circuit, means for translating voltage across said resistor into current oscillations of a predetermined frequency in said oscillator circuit, and means between said timer and oscillator circuit for changing the timing period inversely as the change in oscillation frequency of said oscillator circuit.

2. In induction heating means, a source of alternating current, a heating unit connectedto said source, means connected to said source for rectifying the current thereof, a non-linear'resistor connected to said rectifier, an oscillator circuit connected across said non-linear resistor. the frequency of said oscillator circuit being dependent upon the voltage across the non-linearresistor, a synchronous motor connected to said oscillator circuit, and timing means for vary nl the time period of application of heating current from said electric source to said heating unit in accordance with inverse variation of the frequency of said oscillator circuit.

3. In induction heating apparatus the combination of a source of alternating current, means for rectifying said source current, a non-linear resistor connected across said rectifier, an oscillator circuit connected to said non-linear resistor subject to variation in frequency of 'oscils lation in accordance with variation of the voltage of the source current, a heating circuit. timing means for predetermining the timing period for application of heating energy to said heating means and means connected intermediate the timing means and oscillator circuit for changing the timing period, inversely as the change in frequency of the oscillating circuit.

4. In-induction heating apparatus the combination of a source-of alternating current, means for rectifying said source current, anon-linear resistor connected across said rectifier, a variable linear resistor connected in series with said non-linear resistor, an oscillator circuit connected to said non-linear resistor subject to variation in frequency of oscillation in accordance with variation of said variable resistor and in accordance with variation of the voltage of the source current, a heating circuit, timing means for predetermining the'timing periodfor application of heating energy to said heating means and means connected intermediate the timing means and oscillator circuit for changing the timing period, inversely as the change in frequency of the oscillating circuit.

5. In energy supply means a heating unit, a source of power for said unit, a timer for setting the time period of application of power to said heating unit, and means connected to said timer for modifying the timer period to compensate for changes in power source voltage, said means comprising a resistor having a resistance variable non-uniformly with current connected to the power source, means for establishing a direct current voltageacross said resistor, an oscillator circuit, means for translating voltage across said resistor into our ent oscillations of a predetermined frequency in said oscillator circuit, and means between said timer and oscillator circuit for changing the timing period inversely as the change in oscillation. lator circuit.

6. In induction heating means, a source of current, a heating unit connected to said source, and means for maintaining a substantially uniform flow of power to said heating unit irrespective of source voltage changes, said means including a resistor, the resistance of which varies inversely with change of source voltage, a frequency unit connected to said resistor for developing a frequency change variable directly as the source voltage, and a timer unit limiting the time of power flow to the heating unit directly in accordfrequency of said oscilform flow of power to said heating unit irrespective of source voltage changes, said means comprising a non-linear resistor connected to said source, an oscillator circuit connected across said resistor, a synchronous motor operably connected to said circuit and a timer operably connected to said motor to change the time period of energy supply to said heating unit inversely as the speed of the motor, whereby substantially equal charges of heat are supplied the heating unit.

8. In induction heating means, a source of current, a heating unit connected to said source, and means for maintaining a substantially uniform flow of power to said heating unit irrespective of source voltage changes, said means including a resistor, the resistance of which varies inversely with change of source voltage raised to a power greater than one, a frequency unit connected to said resistor for developing a frequency change variable directly as the source voltage, and a timer unit limiting the time of power flow to the heating unit directly in accordance ance with frequency change in said frequency unit. I

7. In induction heating means, a source of current, a heating unit connected to said source and means .for maintaining a substantially uniwith frequency change in said frequency unit.

9. In induction heating means, a source of current, a heating unit connected to said source, and means for maintaining a substantially uniform flow of power to said heating unit irrespective of source voltage changes, said means including a resistor, the resistance of which varies inversely with change of-source voltage raised to a power preferably between 1.5 and 2.6, a frequency unit connected to said resistor for developing a frequency change variable directly as the source voltage, and a. timer unit limiting the time of power flow to the heating unit directly in accordance with frequency change in said frequency unit.

HAROLD A. S'I'RICKLAND, Ja. 

